Current mirror for mosfet

Discussion in 'Homework Help' started by matlark, Dec 6, 2008.

  1. matlark

    Thread Starter New Member

    Dec 6, 2008
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    Hello,
    Can someone explain the current mirror concept for mosfets?
    thanks
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    I'll be interested in this one, I don't think there is such a thing. As far as I know a current mirror only works with BJTs. I know some FETs (don't think this applies to all) self limit current, as shown in this experiment.
     
  3. steveb

    Senior Member

    Jul 3, 2008
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    The current mirror concept is the same for both mosfets and bipolar junction transistors. The basic idea is to use two identical transistors. One is configured as a diode with the drain and gate (or collector and base for BJT) connected together. When current is driven thru the diode, the diode voltage is used to drive the source/gate terminals (or emiter/base terminals for BJT) of the other transistor. If the transistors are identical and at the same temperature, then the current in the second transistor will match the first transistor that is operating like a diode.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Could you show a schematic for what you're talking about?
     
  5. steveb

    Senior Member

    Jul 3, 2008
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    I was able to find a schematic and analysis in my old electronics notes. Please see attached.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Cool, learned something today. Bet it helps the OP too.
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    If you want to see some gnarly current mirrors, see "CMOS Circuit Design, Layout, and Simulation" by R. Jacob Baker, Harry W. Li, and David E. Boyce, published by IEEE Press, 1988. It has an entire chapter on MOSFET current sources.
     
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